With the remarkable development of information technology (IT), a great variety of portable information communication devices has been popularized. As a result, in the 21st century, we are moving toward a ubiquitous society in which high-quality information service is possible regardless of time and place.
Secondary batteries are very important to realize such a ubiquitous society. Specifically, secondary batteries, which can be charged and discharged, have been widely used as an energy source for wireless mobile devices. In addition, lithium secondary batteries have also been used as an energy source for electric vehicles and hybrid electric vehicles, which have been proposed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
As the range of devices to which secondary batteries are applicable has broadened, as described above, secondary batteries have also been diversified such that the secondary batteries can provide outputs and capacities suitable for devices to which the secondary batteries are applied. In addition, there is a strong need to reduce the size and weight of the secondary batteries.
Secondary batteries may be classified based on the shape of a battery case of each of the secondary batteries into a cylindrical battery configured to have a structure in which an electrode assembly is mounted in a cylindrical metal container, a prismatic battery configured to have a structure in which an electrode assembly is mounted in a prismatic metal container, and a pouch-shaped battery configured to have a structure in which an electrode assembly is mounted in a pouch-shaped case made of a laminated aluminum sheet.
The electrode assembly mounted in the battery case functions as a power generating element, having a positive electrode/separator/negative electrode stack structure, which can be charged and discharged. The electrode assembly may be classified as a jelly-roll type electrode assembly configured to have a structure in which a long sheet type positive electrode and a long sheet type negative electrode, to which active materials are applied, are wound in the state in which a separator is disposed between the positive electrode and the negative electrode, a stacked type electrode assembly configured to have a structure in which a plurality of positive electrodes having a predetermined size and a plurality of negative electrodes having a predetermined size are sequentially stacked in the state in which separators are disposed respectively between the positive electrodes and the negative electrodes, or a stacked/folded type structure, which is a combination of the jelly-roll type electrode assembly and the stacked type electrode assembly.
In recent years, however, a new type of battery cell has been required in accordance with the trend toward a slim type design or various other designs. Specifically, there is a high necessity for a battery cell configured to have a structure in which the battery cell can be efficiently mounted in a device even in the case in which the device does not have sufficient space to receive the battery cell as the result of the reduction in size and thickness of the device.
Conventional devices are manufactured so as to have an approximately rectangular parallelepiped shape. In recent years, however, there have been developed devices having various external shapes. In the case in which a battery cell is configured to have a rectangular parallelepiped shape or a cylindrical shape, it is difficult to efficiently mount the battery cell in such devices having various external shapes.
For example, the sides of a smart phone may be curved to improve grip. However, in the case in which a battery cell having a rectangular parallelepiped shape or a battery pack having a rectangular parallelepiped shape is mounted in a device designed so as to have such curved portions, the efficiency of the efficiency of space utilization in the device may be lowered.
That is, the curved portions of the device have dead spaces, in which the battery cell cannot be mounted. Ultimately, such dead spaces lower the capacity of the device for a given volume.
In addition, heat is generated from the battery cell as the result of high performance of the device, and the lifespan of the battery cell may be considerably reduced due to the heat generated from the battery cell.
Therefore, there is a high necessity for a battery cell configured to have a structure in which the battery cell can be efficiently mounted in a device having various structures such that the amount of dead space is reduced, thereby maximizing the capacity of the battery cell, and in which the reduction in lifespan of the battery cell due to heat generated from the battery cell is prevented.